Pressure drops in oil reservoirs have presented serious problems for operators. In the instance where reservoir pressure drops sufficiently to curtail all oil flow, electric or hydraulic submersible pumps (ESP/HSP) have been one method used to pump oil up the pipe. These pumps are dependent upon either an electrical or hydraulic cable or line. Similarly, data retrieval has been accomplished using electronic pressure/temperature sensors dependent upon either an electrical or fibre optic line.
Deployment of pumps, sensors and their associated electrical and hydraulic lines presents significant problems. Typically, two methods of ESP/HSP or data sensor deployment have been employed: tubing deployment and wireline deployment. Tubing deployment is heavy, bulky and time-consuming, requiring the cable or line to be secured to each tubing joint as it is added to the string. Wireline deployment is lighter and less time-consuming. However, wireline deployed ESP/HSP systems cannot be used in wells where a deviated bore is used, and the ESP/HSP can become stuck. Due to the environment in which it is operating, the life cycle of any equipment located in the tubing is short. This means retrieval and replacement on a regular basis, which is expensive and time-consuming, due to the fact that equipment can only be retrieved by pulling back the tubing. Certain wells which require artificial lift may prove to be non-viable using existing ESP/HSP deployment and servicing methods.
A third option is required whereby cable or line dependent equipment can be deployed and retrieved at minimal added cost to the operator. The means of deployment should ideally be applicable to both new and existing Christmas trees, in order to provide a more economically viable means of deploying or servicing artificial lift or sensor equipment.
The present invention provides a horizontal Christmas tree comprising a tubing hanger having a lateral production fluid outlet communicating with an axial through bore, the axial through bore being sealed above the lateral production outlet in use by a plug, the tubing hanger being landed in a substantially vertically extending bore in the christmas tree; an internal tree cap being installed within the vertically extending bore above the tubing hanger, characterised in that a coiled tubing hanger is landed within the tubing hanger and is adapted to suspend coiled tubing within the well, the coiled tubing carrying power or signal lines to downhole equipment, these power or signal lines exiting the tree upwardly through the cap. With such coiled tubing deployed cable dependent equipment, wells requiring artificial lift can be produced more economically than with other methods of artificial lift and ESP/HSP deployment, there being significant savings in time and equipment costs. The invention is particularly advantageous as the downhole power or signal lines and the pump or other equipment can be installed or replaced without disturbing the tree or tubing hanger.
The coiled tubing hanger may serve as the plug, for example replacing a crown plug previously installed in the tubing hanger through bore.
Preferably, an upper wireline plug of an otherwise standard horizontal Christmas tree is replaced with an access plug including power or signal lines running through it, allowing connection to the power and signal lines of the coiled tubing, without disturbing the tree cap. The invention may therefore be used to convert a former natural drive well for ESP/HSP operation, once its reservoir has lost pressure.